Internal combustion engine

ABSTRACT

An in-line four-cylinder internal combustion engine wherein exhaust ports ( 8, 9 ) of a pair of cylinders positioned at the center are connected to a single merged exhaust port ( 11 ) and this merged exhaust port ( 11 ) is connected through a first exhaust pipe ( 19 ) to a catalytic converter ( 18 ). On the other hand, exhaust ports ( 7, 10 ) of pairs of cylinders positioned at the two ends are connected through a second exhaust pipe ( 21 ) to a catalytic converter ( 18 ). A length of the first exhaust pipe ( 19 ) from the merged exhaust port ( 11 ) to the catalytic converter ( 18 ) is made shorter than the length of the second exhaust pipe ( 21 ) from the exhaust ports ( 7, 10 ) to the catalytic converter ( 18 ).

TECHNICAL FIELD

The present invention relates to an internal combustion engine.

BACKGROUND ART

In in-line four-cylinder internal combustion engines, there is known aninternal combustion engine in which a pair of cylinders positioned atthe center have exhaust ports merged into a single merged exhaust portinside the cylinder head and opening on the side wall surface of thecylinder head and in which pairs of cylinders positioned at the two endshave exhaust ports opening on the side wall surface of the cylinder headat the two sides of the opening part of the merged exhaust port asindependent exhaust ports (see Japanese Patent Publication (A) No.2003-176722).

In this internal combustion engine, an exhaust manifold common to allcylinders is attached to the side wall surface of the cylinder head.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an optimum layout andstructure of a first exhaust pipe connected to a merged exhaust port anda second exhaust pipe connected to a pair of independent exhaust portswhen constructing a double system of these exhaust pipes in the case ofan internal combustion engine having one merged exhaust port and a pairof independent exhaust ports such as explained above.

According to the present invention, there is provided an in-linefour-cylinder internal combustion engine wherein exhaust ports of a pairof cylinders positioned at the center merge inside a cylinder head intoa single merged exhaust port and open on a side wall surface of thecylinder head, exhaust ports of pairs of cylinders positioned at the twoends open on the side wall surface of the cylinder head at the two sidesof an opening part of the merged exhaust port as independent exhaustports, and the opening part of said merged exhaust port is connectedthrough a first exhaust pipe to either an exhaust inflow part of acatalytic converter or an exhaust inflow part of an exhaustturbocharger, the opening parts of said pair of independent exhaust portbeing connected through a second exhaust pipe merged midway to the sameexhaust inflow part, and a length of the first exhaust pipe from thecorresponding opening part to said exhaust inflow part being madeshorter than the length of the second exhaust pipe from thecorresponding opening parts to said exhaust inflow part.

In the present invention, the exhaust gas temperature of the exit partof the merged exhaust port is higher than the exhaust gas temperature atthe exit part of the independent exhaust port. The higher temperatureexhaust gas is fed through the first exhaust pipe with the shorter pipelength, that is, the smaller temperature drop, to a catalytic converteror exhaust turbocharger. That is, since the first exhaust pipe can feedhigh temperature exhaust gas to the catalytic converter or exhaustturbocharger, warmup of the catalyst can be promoted or the efficiencyof the exhaust turbocharger can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan cross-sectional view of a cylinder head.

FIG. 2 is a cross-sectional view of a cylinder head as seen along II-IIof FIG. 1.

FIG. 3 is a perspective view showing the contour shapes of exhaustports.

FIG. 4 is a front view of the side wall surface of a cylinder head.

FIG. 5 is a perspective view of an internal combustion engine.

FIG. 6 is a side view of the internal combustion engine shown in FIG. 5.

FIG. 7 is a side view of another embodiment of an internal combustionengine.

BEST MODE FOR WORKING THE INVENTION

FIG. 1 and FIG. 2 show a cylinder head 1 integrally cast from forexample an aluminum alloy. Note that the circles shown by broken linesin FIG. 1 show the positions of the No. 1 cylinder #1, No. 2 cylinder#2, No. 3 cylinder #3, and No. 4 cylinder #4. Therefore, it is learnedthat the internal combustion engine provided with the cylinder head 1shown in FIG. 1 is an in-line four-cylinder internal combustion engine.In FIG. 1, 2 shows a valve port opened and closed by an intake valve,while 3 shows a valve port opened and closed by an exhaust valve.Therefore, it is learned that each cylinder #1, #2, #3, and #4 isprovided with a pair of intake valves and a pair of exhaust valves.

Note that the cylinder head 1 actually has cooling water passagesextending along complicated paths, support parts of the valve trains,insertion parts for spark plugs, insertion parts for fuel injectors,etc. formed in it, but in FIG. 1 and FIG. 2, these are omitted.

The cylinder head 1 has side wall surfaces 4 and 5 substantially inparallel at the two sides of a plane including the cylinder axial linesof the cylinders #1, #2, #3, and #4. The intake ports 6 of the cylinder#1, #2, #3, and #4 formed in the cylinder head 1 open on the side wallsurface 4.

Further, the cylinder head 1 has exhaust ports 7 of the No. 1 cylinder#1, exhaust ports 8 of the No. 2 cylinder #2, exhaust ports 9 of the No.3 cylinder #3, and exhaust ports 10 of the No. 4 cylinder #4 formed init. FIG. 3 is a perspective view of the contour shapes of such exhaustports. As will be explained from FIG. 1, the pairs of exhaust ports 7,8, 9, and 10 are separate near the corresponding pairs of valve ports 3,but when leaving the valve ports 3 a bit become single exhaust ports.

Now, as will be understood from FIG. 1, the exhaust ports of the pair ofcylinders positioned at the center, that is, the exhaust ports 8 of theNo. 2 cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3 aremerged inside the cylinder head 1 to form a single merged exhaust port11. This merged exhaust port 11 is extended to the side wall surface 5of the cylinder head 1. In FIG. 1, if the plane extending through thecenter between the No. 2 cylinder #2 and No. 3 cylinder #3 in thecylinder axial line direction and perpendicular to the plane includingthe cylinder axial lines of the cylinders #1, #2, #3, and #4 is referredto as the “symmetrical plane K-K”, the exhaust ports 8 of the No. 2cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3 arearranged symmetrically with respect to the symmetrical plane K-K. Themerged exhaust port 11 extends along the symmetrical plane K-K to theside wall surface 5 of the cylinder head 1.

On the other hand, the exhaust ports of the pairs of cylinderspositioned at the two ends, that is, the exhaust ports 7 of the No. 1cylinder #1 and the exhaust ports 10 of the No. 4 cylinder #4, are alsoarranged symmetrically with respect to the symmetrical plane K-K. Inthis case, the exhaust ports 7 of the No. 1 cylinder #1 extend from theNo. 1 cylinder #1 toward the merged exhaust port 11, then extend alongthe merged exhaust port 11 separated from the merged exhaust port 11 bya thin wall 12 at the side of the merged exhaust port 11 until the sidewall surface 5 of the cylinder head 1, while the exhaust ports 10 of theNo. 4 cylinder #4 extend from the No. 4 cylinder #4 toward the mergedexhaust port 11, then extend along the merged exhaust port 11 separatedfrom the merged exhaust port 11 by a thin wall 13 at the side of themerged exhaust port 11 until the side wall surface 5 of the cylinderhead 1.

As shown from FIG. 1 to FIG. 4, the merged exhaust port 11 opens on theside wall surface 5 of the cylinder head 1 at 14, while the pairs ofindependent exhaust ports, that is, the exhaust ports 7 of the No. 1cylinder #1 and the exhaust ports 10 of the No. 4 cylinder #4, open atthe two sides of the opening part 14 of the merged exhaust port 11 atthe side wall surface 5 of the cylinder head 1 as shown by 15 and 16.Note that as will be understood from FIG. 3 and FIG. 4, the opening areaof the opening part 14 of the merged exhaust port 11 is larger than theopening part 15, 16 of the pairs of independent exhaust ports 7, 10.

FIG. 5 shows part of an internal combustion engine, while FIG. 6 is aside view of the internal combustion engine shown in FIG. 5. Note thatin FIG. 5 and FIG. 6, 17 shows a cylinder block, while 18 shows acatalytic converter. As will be understood from FIG. 4, FIG. 5, and FIG.6, according to the present invention, the opening part 14 of the mergedexhaust port 11 is connected through a first exhaust pipe 19 to anexhaust inflow part 20 of the catalytic converter 18, while the openingparts 15, 16 of the pairs of independent exhaust ports 7, 10 areconnected through a second exhaust pipe 21 merged midway to the exhaustinflow part 20 of the catalytic converter 18. In this case, the pipelength of the first exhaust pipe 19 from the corresponding opening part14 to the exhaust inflow part 20 is formed shorter than the pipe lengthof the second exhaust pipe 21 from the corresponding opening parts 15,16 to the exhaust inflow part 20.

Explaining this in slightly more detail, the first exhaust pipe 19 andthe second exhaust pipe 21 are bent downward in the middle of theirdistance from the corresponding opening parts 14, 15, 16 to the exhaustinflow part 20. The second exhaust pipe 21 extends along the outside ofthe first exhaust pipe 19 after the branches of the second exhaust pipe21 merge at the outside of the first exhaust pipe 19. Further, thecatalytic converter 18 is provided with a pair of exhaust inflowopenings 22, 23. The first exhaust pipe 19 and second exhaust pipe 21are connected to corresponding exhaust inflow openings 22, 23.

However, in this embodiment according to the present invention, thefiring sequence of the cylinders is made #1→*#3→#4→#2 or #1→#2→#4→#43.In both cases, the pairs of cylinders at every other place in the firingsequence become the pair of the No. 2 cylinder #2 and No. 3 cylinder #3positioned at the center and the pair of the No. 1 cylinder #1 and No. 4cylinder #4 positioned at the two ends. In this case, if all of theexhaust ports were merged inside the cylinder head 1 or if all of theexhaust ports were opened inside an exhaust manifold with a manifoldchamber extending along the side wall surface 5 of the cylinder head 1,the positive pressures generated inside exhaust ports at the time of anexhaust stroke of a certain cylinder would act at the time of theexhaust stroke in the exhaust ports of the cylinder next fired and as aresult the problem would arise of the exhaust action of the burned gasfrom the combustion chamber being impaired.

As opposed to this, as shown in the embodiment of the present invention,if merging the exhaust ports of only the cylinders at every other placein the firing sequence, that is, merging the exhaust ports 8 of the No.2 cylinder #2 and the exhaust ports 9 of the No. 3 cylinder #3, mergingthe exhaust ports 7 of the No. 1 cylinder #1 and the exhaust ports 10 ofthe No. 4 cylinder #4, and keeping the merged exhaust passages, that is,the exhaust passage in the first exhaust pipe 19 and the exhaust passagein the second exhaust pipe 21, separate until the exhaust inflow part 20of the catalytic converter 18, the positive pressure generated insidethe exhaust ports of the other cylinders will not act on the exhaustports where an exhaust action is being performed at the time of anexhaust stroke, therefore burned gas will no longer be exhausted wellfrom the combustion chamber. That is, exhaust interference can beprevented, so a high charging efficiency can be secured.

Now, here, if comparing the flow of exhaust gas in the merged exhaustport 11 and the flows of exhaust gas in the independent exhaust ports 7,10, exhaust gas flows to the exit part of the merged exhaust port 11 twotimes in each cycle, while exhaust gas only flows to the exit parts ofthe independent exhaust ports 7, 10 once in each cycle. Therefore, thewall temperature of the exit part of the merged exhaust port 11 becomesconsiderably higher than the wall temperatures of the exit parts of theindependent exhaust ports 7, 10. Further, the lengths of the passages ofthe exhaust ports 7, 10 are long, so the exhaust gas exhausted insidethe exhaust ports 7, 10 is considerably cooled inside the cylinder head1. As opposed to this, the length of the passage of the merged exhaustport 11 is short, so the exhaust gas exhausted inside the merged exhaustport 11 is not cooled much at all inside the cylinder head 1. Therefore,the temperature of the exhaust gas flowing out from the opening part 14of the merged exhaust port 11 becomes considerably higher than thetemperature of the exhaust gas flowing out from the opening parts 15, 16of the independent exhaust ports 7, 10.

On the other hand, as explained above, the length of the first exhaustpipe 19 is shorter than the length of the second exhaust pipe 21,therefore when exhaust gas flows inside the exhaust pipes 19, 21, theamount of drop of the exhaust gas temperature in the first exhaust pipe19 is smaller than the amount of drop of the exhaust gas temperature inthe second exhaust pipe 21. In this way, high temperature exhaust gas isexhausted from the merged exhaust port 11 into the first exhaust pipe19. At this time, the amount of drop of the exhaust gas temperature inthe first exhaust pipe 19 is small, so the temperature of the exhaustgas flowing from the first exhaust pipe 19 into the catalytic converter18 becomes considerably high. Therefore, it is possible to quickly warmup the catalyst in the catalytic converter 18.

On the other hand, the amount of exhaust gas flowing out from theopening part 14 of the merged exhaust port 11 becomes two times theamount of exhaust gas from the opening part 15, 16 of each of theindependent exhaust ports 7, 10, so the opening area of the opening part15 of the merged exhaust port 11 is formed larger than the opening areaof the opening part 15, 16 of each of the independent exhaust ports 7,10. Therefore, the flow area of the first exhaust pipe 19 also is formedlarger than the flow area of each of the two branch parts 21 a of thesecond exhaust pipe 21. As will be understood from FIG. 5, in thisembodiment according to the present invention, to hold the temperatureof the first exhaust pipe 19 at as high a temperature as possible andprevent the temperature of the exhaust gas flowing in the first exhaustpipe 19 from dropping as much as possible, the first exhaust pipe 19 issurrounded at its outside by the second exhaust pipe 21.

FIG. 7 shows another embodiment. In this embodiment, the first exhaustpipe 19 and second exhaust pipe 21 are connected to the exhaust inflowpart 25 of the exhaust turbocharger 24. In this case, the first exhaustpipe 19 and the second exhaust pipe 21 are bent upward from thecorresponding opening parts 14, 15, 16 toward the exhaust inflow part25, while the second exhaust pipe 21 extends along the outside of thefirst exhaust pipe 19 after the branches of the second exhaust pipe 21merge at the outside, of the first exhaust pipe 19.

In this embodiment as well, the length of the first exhaust pipe 36 fromthe corresponding opening part 14 to the exhaust inflow part 25 isformed shorter than the length of the second exhaust pipe 21 from thecorresponding opening parts 15, 16 to the exhaust inflow part 25.Further, the exhaust turbocharger 24 is comprised of a twin entry typeturbocharger provided with a pair of exhaust inflow openings 26, 27. Thefirst exhaust pipe 19 and second exhaust pipe 21 are connected to therespective corresponding exhaust inflow openings 26, 27.

In this embodiment as well, high temperature, that is, high pressure,exhaust gas is fed from the first exhaust pipe 19 into the exhaustturbocharger 24, so the speed of the exhaust turbocharger 24 can beraised and therefore the efficiency of the exhaust turbocharger 24 canbe enhanced. Note that in FIG. 5 and FIG. 6, instead of the catalyticconverter 18, it is possible to attach an exhaust turbocharger 24. Inthis case, a catalytic converter 18 can also be connected to the exhaustoutflow part of the exhaust turbocharger 24. Further, similarly, in FIG.7, a catalytic converter 18 can be attached instead of the exhaustturbocharger 24.

LIST OF REFERENCE NUMERALS

-   -   1 cylinder head    -   7,8,9,10 exhaust port    -   11 merged exhaust port    -   14,15,16 opening part    -   18 catalytic converter    -   19 first exhaust pipe    -   20,25 exhaust inflow part    -   21 second exhaust pipe    -   22,23,26,27 exhaust inflow openings    -   24 exhaust turbocharger

1. An in-line four-cylinder internal combustion engine wherein centralexhaust ports of a pair of cylinders positioned at the center open on aside wall surface of the cylinder head, exhaust ports of a pair ofcylinders positioned at the two ends open on the side wall surface ofthe cylinder head at the two sides of the opening part of the centralexhaust ports as independent exhaust ports, and the opening part of saidcentral exhaust ports is connected through a first exhaust pipe to anexhaust inflow part of a catalytic converter, the opening parts of saidpair of independent exhaust ports being connected through a secondexhaust pipe merged midway to the same exhaust inflow part, and a lengthof the first exhaust pipe from the corresponding opening part to saidexhaust inflow part being made shorter than the length of the secondexhaust pipe from the corresponding opening parts to said exhaust inflowpart, characterized in that the central exhaust ports (8, 9) of a pairof the cylinders (#2, #3) positioned at the center merge inside thecylinder head (1) into a single merged exhaust port (11) which has thesingle opening part (14) connected to the first exhaust pipe (19), andthe exhaust ports (7, 10) of a pair of the cylinders (#1, #4) at the twoends extend along the merged exhaust port (11) separated from the mergedexhaust port (11) by corresponding thin walls (12, 13) at the sides ofthe merged exhaust port (11) until the side wall surface (5) of thecylinder head (1).
 2. An internal combustion engine as set forth inclaim 1, wherein the catalytic converter (18) is provided with a pair ofexhaust inflow openings (22, 23), and said first exhaust pipe (19) andsecond exhaust pipe (21) are connected to the corresponding exhaustinflow openings (22, 23).
 3. An internal combustion engine as set forthin claim 1, wherein an exhaust turbocharger (24) is provided in place ofa catalytic converter and is provided with a pair of exhaust inflowopenings (26, 27), and said first exhaust pipe (19) and second exhaustpipe (21) are connected to the corresponding exhaust inflow openings(26, 27).
 4. An internal combustion engine as set forth in claim 1,wherein said first exhaust pipe (19) and second exhaust pipe (21) arebent in the middle of the distance from the corresponding opening parts(14, 15, 16) toward said exhaust inflow part toward the same direction,and said second exhaust pipe (21) extends along the outside of the firstexhaust pipe (19) after branches of said second exhaust pipe (21) mergeat the outside of the first exhaust pipe (19).
 5. An internal combustionengine as set forth in claim 1, wherein the opening area of the openingpart (14) of said merged exhaust port (11) is larger than the openingarea of the opening part (15, 16) of each independent exhaust port (7,10).